Smaller shop radiant heat

[bdymnjm]

I got all carried away seeing these big shops going up and the radiant floor heat. So knowing that pex needs to be installed in the floor I had a supply house provide the pex and the guy helped lay it out. Nice guy, friend of a friend and he also provided me some data on heat loss. Time flies and I haven't finished the insulation or heat. Now my dilemma is a heat source. My wife is really against propane. I would like oil but it doesn't seem practical for my needs.

I wonder if I can use a small on demand electric domestic water heater?

I will post the info he prepared for heat loss. I think it will be best to be able to set temp to just maintain 40 to 50 and use another source to bring it up a little more on demand when working.

 

[bdymnjm]

The heat data

 

[Vtor]

I'm in similar boat, deteached garage, limited fuel sources.

Considering a small electric water heater to run when I use the garage. No plans to heat full time in my case. My concern is duty cycle on those water heaters.. they are very cheap, like sub $200. Add circulator, expansion tank, low water cut off, air vent.. run it.

 

[Firebrick43]

Some people use resistance heat, I would never recommend it if possible. The electric on demand heaters may be small but their amperage demands are not. A 14K watt requires 2 30amp 240 circuits(60 amps total). Tank type water heaters are a poor choice with low life span in a heating situation.

What is the wifes hang up on propane? Set up right it is the best choice most places when natural gas is not available?

Vtor, pick another form of heat if your not going to heat full time. A slab takes several days to bring to temp. Most people actually are pretty confortable in shop with a floor heated to 55 degrees with a Long sleeve t shirt on due to the somewhat warm floor.

 

[bdymnjm]

I'm in similar boat, deteached garage, limited fuel sources.

Considering a small electric water heater to run when I use the garage. No plans to heat full time in my case. My concern is duty cycle on those water heaters.. they are very cheap, like sub $200. Add circulator, expansion tank, low water cut off, air vent.. run it.

What I realize now is it would be hours probably to warm the shop from 30f to 50 or more so unless a large b.t.u. Input might help I won't just walk in and get warm. I can set a tiny electric cube heater on low and hold 30 (windy and 20 or less) so when I'm insulated better 1500 to 3000 watts heated water going in the floor might be good. Some good setups here on GJ so we should be able to figure out a setup.

You think the duty cycle will be important? I was thinking it won't hit a high temp so maybe no harm? I didn't look into it..

Jim

 

[Firebrick43]

3000 watts even in a small well insulated space is a pipe dream unless every detail is sorted out from the beginning

 

[Don1357]

People here will tell you that it will never work, and yet here un Alaska I have been to two toasty shop heated with one. We do insulate or slabs and put angled insulation away from the slab. Did you insulate?

The fly in your ointment is your desire for intermittent heat, radiant doesn't work that way. It is more like filling a leaky pool; it takes forever to put 20,000 gallons of water there but once filled up it only takes a bit of water to keep it full. Radiant is exactly the same way; it will take you days to fill that thermal mass and after that you are better off keeping it full or else you would have squandered all the energy it took to get there.

 

[Firebrick43]

People here will tell you that it will never work, and yet here un Alaska I have been to two toasty shop heated with one. We do insulate or slabs and put angled insulation away from the slab. Did you insulate?

The fly in your ointment is your desire for intermittent heat, radiant doesn't work that way. It is more like filling a leaky pool; it takes forever to put 20,000 gallons of water there but once filled up it only takes a bit of water to keep it full. Radiant is exactly the same way; it will take you days to fill that thermal mass and after that you are better off keeping it full or else you would have squandered all the energy it took to get there.

I looked at the pictures before I said it wouldn't work. He did insulate the slab ok but did not add wings nor is the 4' block stub walls insulated and I would dare to say the slab is not uncoupled from the wall at the edges nor the footer.

 

[jlv03]

I use a 6kW electric boiler from Thermolec for my 24' x 28' attached garage floor heat. Works just fine, but there is nothing quick about bringing up the heat.

http://thermolec.com/en/productView.aspx?type=product&id=62

The problem with going with a water heater is, if you are putting any sort of anti-freeze in the water, you have to have a giant tank of anti-freeze that costs a fair amount of money. You also need the space for the tank vs. a boiler you can hang on a wall.

 

[tdkkart]

What I realize now is it would be hours probably to warm the shop from 30f to 50 or more so unless a large b.t.u. Input might help I won't just walk in and get warm.

Here's where you may be going wrong from the start.

With in floor heating you do not roll it back or shut it down at night or during the week and expect to crank it back up when it's time to work. As you suspect, to get it from 30 degrees to 50 degrees will take hours. You're working with a huge mass of concrete, it doesn't change temperatures quickly no matter what you heat it with.
I've run electric in floor heat in a 1200sqft building for 13 years. I turn it on Nov 1st or so and turn it off April 1st. Set the thermostat and forget it. Is it cheap?? Nope, but it's the most comfortable shop I've ever worked in.

 

[Vtor]

I know well that instant heat w massive concrete slab is not instant, but you CAN plan around it. It's Friday, you plan on doing work over the weekend.. bam, turn it on night before, by the following morning, it wont be freezing cold!

Personally, could not justify keeping it on full time, just a waste. Otherwise, woudl need more efficient heat source, like heat pump or similar.

 

[tdkkart]

Personally, could not justify keeping it on full time, just a waste. Otherwise, woudl need more efficient heat source, like heat pump or similar.

I'm in my shop almost nightly, for at least a couple hours, plus 4-6hrs at least one if not both days on the weekends.
If I had any type of heat that I had to wait on to heat up I'd just skip it.

 

[Vtor]

Clearly different usage patterns, so system woudl have to be designed accordingly.

Stick a mini split on wall and call it a day. Kick on radiant for extra comfort.

 

[PWC Repair]

Guys, insulate the building well and you're golden. I heat my 30x48x12 with a 40 gallon electric water heater. We're in a stretch of 20's for the highs and single digit nights and it's currently 53* in my shop. Check it out in my build thread below! I researched quite a bit and pretty much came to the conclusion it won't work.........which is why I did it anyway and below freezing for 48 hours has it running quite a bit. BUT we usually don't have weather like this either.

 

[Jackfre]

Always best to have these things laid out on the way in, but, so it goes. With an 8000 btu load you might be able to do it with an electric boiler. Notice I said boiler not on-demand water heater. You will probably be oversized anyway on the input side. I do not follow electric boilers so cannot make a recommendation on manuf. I do know some of the people at Emmax and will inquire with them if you would like. Let me know. Radiant isn’t turn it on and be worm. You have lead/lag issues on a slab and you can’t throw any more heat at it than it can emit. Perhaps a wireless t-stat so you can anticipate your use and operate accordingly. You do have about the highest electric rates in the country so be careful here.

 

[Montucky]

I heat my entire house with a small on demand takagi water heater. We have a very small mechanical room that has two of these on demand units. One for the floor and one for the potable water. It’s 0 degrees right now outside and my house is 70 inside. It could be warmer if I cranked it up. It looks like the tk110 takagi is just over 500$ from supply house dot com. First heater lasted a decade and would have went longer if I cleaned it more regularly. When I had the new one installed I had the guy hook up flush valves so I can flush easily. I’m still on original takagi for potable water.

As others have mentioned I just leave it on in winter and keep house at 70. Heat bill with power and gas is max 120$ house is @1400 sqft with second level. The second level has cadet wall heaters that I have never turned on.

 

[bdymnjm]

The perimeter is done with tuff r 1" to at least break the thermal Bridge to the block wall. Other than the block wall it is going to be well insulated. Like I said the insulation is far from done and the 1500 watt heater is able to keep it above freezing in some cold snaps we had. 3 heaters kept it at 60 when I needed to dry some paint on a frame, and they didn't run continuous. I am not trying to say anybody is wrong. I live in a climate where its not comfortable to grab tools and work at ambient temperatures a few months a year. You get used to it. If I am out of the wind and 45f thats pretty good unless I'm trying to do body filler and paint.

I think its important for folks to know that throwing pex in floor won't give on demand heat and therefore they should plan whether they want to spend money to heat full time, plan use ahead, or use dual heat sources.

The system will be the same except the heat source right? That can be upgraded if needed.

Thank you for all the help and comments.

Jim